Totally confused about cookie free domains

I know this may seem basic to some but I have read every tutorial about implementing cookieless domains on WordPress. I’ve set up a domain just to run for my static content domain.

After this I get pretty lost fast. I saw the commands to add to wp-config file on many tutorials but then I was an idiot and didn’t bookmark them and I can’t find it so that info would be helpful ??

After that the tutorials sad make sure you add something like blog_info(something about templates I think) to your WordPress file but they all seem to stop at that line and don’t say where or what the actually say inside the blog info line.

Lastly, once I get that all working properly do I then need to upload all my image files to the cookieless domain? I’m guessing I do but most articles don’t say anything about that.

Thank you in advance.